Prostheses for implantation in blood vessels or other similar organs of the living body are, in general, well known in the medical art. For example, prosthetic vascular grafts constructed of biocompatible materials have been employed to replace or bypass damaged or occluded natural blood vessels. In general, endovascular grafts typically include a graft anchoring component that operates to hold a tubular graft component of a suitable graft material in its intended position within the blood vessel. Most commonly, the graft anchoring component is one or more radially compressible stents that are radially expanded in situ to anchor the tubular graft component to the wall of a blood vessel or anatomical conduit. Thus, endovascular grafts are typically held in place by mechanical engagement and friction due to the opposition forces provided by the radially expandable stents.
Grafting procedures are also known for treating aneurysms. Aneurysms result from weak, thinned blood vessel walls that “balloon” or expand due to aging, disease and/or blood pressure in the vessel. Consequently, aneurysmal vessels have a potential to rupture, causing internal bleeding and potentially life threatening conditions. Grafts are often used to isolate aneurysms or other blood vessel abnormalities from normal blood pressure, reducing pressure on the weakened vessel wall and reducing the chance of vessel rupture. As such, a tubular endovascular graft may be placed within the aneurysmal blood vessel to create a new flow path and an artificial flow conduit through the aneurysm, thereby reducing if not nearly eliminating the exertion of blood pressure on the aneurysm.
In general, rather than performing an open surgical procedure to implant a bypass graft that may be traumatic and invasive, endovascular grafts which may be referred to as stent-grafts are preferably deployed through a less invasive intraluminal delivery procedure. More particularly, a lumen or vasculature is accessed percutaneously at a convenient and less traumatic entry point, and the stent-graft is routed through the vasculature to the site where the prosthesis is to be deployed. Intraluminal deployment is typically effected using a delivery catheter with coaxial inner and outer tubes arranged for relative axial movement. For example, a self-expanding stent-graft may be compressed and disposed within the distal end of an outer catheter tube distal of a stop fixed to the inner member. The catheter is then maneuvered, typically routed through a body lumen until the end of the catheter and the stent-graft are positioned at the intended treatment site. The stop on the inner member is then held stationary while the outer tube of the delivery catheter is withdrawn. The stop prevents the stent-graft from being withdrawn with the sheath. As the sheath is withdrawn, the stent-graft is released from the confines of the sheath and radially self-expands so that at least a portion of it contacts and substantially conforms to a portion of the surrounding interior of the lumen, e.g., the blood vessel wall or anatomical conduit.
In recent years, to improve optimal control and alignment during deployment and positioning of a stent-graft, various tip capture spindles have been incorporated into the delivery system utilized for percutaneously delivering the stent-graft prosthesis. Tip capture involves restraining the proximal end stent of the stent-graft in a radially compressed configuration in conjunction with the main body restraint achieved by other delivery system components, such as a tubular cover shaft or sheath. The tip capture spindle can be activated at any time during stent-graft deployment to suit any number of system characteristics driven by the therapy type, stent-graft type, or specific anatomical conditions that may prescribe the release timing. Typically, the tip capture release is activated after some or all the main stent-graft body release, and thus provides a mean of restraining the stent-graft during positioning and any re-positioning. Additional restraint of the stent-graft is a key characteristic when the operator is attempting to accurately position the stent relative to an anatomical target. The tip capture restraint also aids in reducing an abrupt force of expansion when the stent-graft is released from the graft cover or sheath.
For example, U.S. Patent Application Publication No. 2006/0276872 to Arbefuielle et al. and U.S. Patent Application Publication No. 2009/0276027 to Glynn et al., both herein incorporated by reference in their entirety, describe tip capture mechanisms that restrain the proximal end stent of the stent-graft while the remainder of the stent-graft expands, then releases the proximal end stent. The proximal end stent (sometimes also referred to as the anchor stent) is attached to the graft material of the stent-graft so as to have an “open web” or “free flow” proximal end configuration in which the proximal endmost crowns thereof extend past or beyond the graft material such that the proximal endmost crowns are exposed or bare, and thus free to interact with a tip capture mechanism and couple the stent-graft prosthesis to the delivery system. FIGS. 1A and 1B illustrate a delivery system 10 having a tip capture spindle 12 designed to couple or interact with a stent-graft 14 having an open web or free flow proximal end configuration 16. More particularly, endmost crowns 18 engage or hook around retractable arms or retainer elements 20 of the tip capture spindle 12. Delivery system 10 includes at least three concentric shafts, namely an outer delivery sheath or graft cover 22, an intermediate shaft 24 coupled to tip capture spindle 12, and an elongate inner shaft 26 coupled to distal tip assembly 28. When graft cover 22 is retracted to allow stent-graft 14 to self-expand, endmost crowns 18 of the end stent 15 remain hooked around tip capture retainer elements 20, as shown in FIG. 1A. To release end stent 15, intermediate shaft 24 coupled to tip capture spindle 12 is retracted longitudinally relative to inner shaft 26 to retract tip capture spindle 12 such that end stent 15 is released from tip capture spindle 12 and allowed to self-expand, as shown in FIG. 1B. The Captivia Delivery System manufactured by Medtronic Vascular, Inc. of Santa Rosa, Calif. is one example of a delivery system having a tip capture mechanism as described above, which may be utilized for delivering endovascular stent-grafts such as the Valiant Thoracic Stent-graft manufactured by Medtronic Vascular, Inc. of Santa Rosa, Calif.
Tip capture mechanisms have improved accuracy of deployment of self-expanding stent-grafts. However, tip capture mechanisms known in the art require two or more concentric shafts, in addition to the outer sheath, such as intermediate shaft 24 and elongate inner shaft 26 described above with respect to FIG. 1 to retract the tip capture spindle and fully deploy the stent-graft. Two or more concentric shafts within the delivery system may cause several trackability and deployment challenges. More particularly, two or more concentric shafts increase the delivery or crossing profile of the delivery system. In addition, release forces associated with a delivery system having two or more concentric shafts that slide longitudinally relative to each other are relatively higher than a delivery system not requiring two or more concentric shafts because frictional forces between the two concentric shafts must be overcome to release the stent-graft from the tip capture spindle. Further, premature release of the stent-graft may occur when a user is attempting to maneuver the delivery system during repositioning of the stent-graft. When positioning or repositioning the delivery system, the user must push or pull the delivery system longitudinally. Due to the force required to push or pull the delivery system through tortuous vessels, the concentric shafts 24, 26 of the tip capture system may slide relative to each other, thereby causing premature release of the stent-graft from the tip capture spindle. Embodiments hereof relate to a delivery system having a tip capture mechanism to allow for partial deployment and repositioning of the stent-graft, wherein the delivery system more efficiently retracts the tip capture spindle.